Low-temperature exhumation history of the eastern Musgrave Province
Low-temperature thermochronology comprises a series of dating techniques to examine the low-temperature thermal evolution and shallow crustal exhumation history of an area. The various techniques are effective for different temperature ranges dependent upon the closure temperatures and or closure temperature windows for the different thermal properties of a mineral that is being measured. This article summarises the results of our recently published study into the low-temperature thermal history of the Musgrave Province, South Australia (Glorie et al. 2017). We utilised apatite fission track thermochronology and apatite and zircon (U–Th–Sm)/He thermochronology to constrain the low-temperature thermal evolution of a portion of the Musgrave Province. This article also aims to illustrate the use of low-temperature thermochronology to understand the exhumation history of a geological terrane.
Low-temperature thermochronology methods
Apatite fission track thermochronology is based on the measurement of nuclear damage trails, or fission tracks, which are caused by the spontaneous fission decay of 238Uranium (238U) within the crystal lattice (Wagner and Van den haute 1992). The tracks are only completely retained at temperatures ≤60 °C. Between ~60 °C and ~120 °C, the fission tracks shorten or anneal. Above ~120 °C the crystal lattice is able to completely repair itself from radiation damage, removing the tracks (Green et al. 1985). In 2015 the Department of Earth Sciences at the University of Adelaide successfully obtained funding under the Australian Research Council Linkage Infrastructure Equipment and Facilities scheme to install an Autoscan System for semi-automatic fission track analysis. This has enabled the collection of a large database of thermochronological measurements in a number of studies across South Australia and internationally (e.g. Hall et al. 2016a, 2016b).
The apatite fission track method is complemented by analysis of apatite and, if available, zircon, via the (U–Th–Sm)/He method. Apatite and zircon (U–Th–Sm)/He low-temperature thermochronology is based on the diffusivity of radiogenic 4He through a mineral crystal lattice during certain temperature ranges. For apatite, this method records the timing of thermal events between ~45 °C and ~75 °C (Ehlers and Farley 2003), whereas zircon grains record cooling ages of between ~130 °C and ~200 °C (Wolfe and Stockli 2010).
These techniques can be complemented by other thermochronological methods such as 40Ar/39Ar to understand the thermal history of a region. The choice of methods depends upon the mineralogical assemblages available within the rock types being studied. These techniques are particularly powerful when a suite of samples are collected along and across structures as this allows the timing of fault-induced exhumation to be estimated.
The Musgrave Province is an east–west-trending basement inlier located in central Australia, which is bounded by Neoproterozoic to Mesozoic sedimentary rocks of the Amadeus, Officer, and Eromanga basins (Wade et al. 2008; Raimondo et al. 2010; Howard et al. 2015; Smithies et al. 2015). Previous studies have focused on the magmatic and high-grade metamorphic histories of the Musgrave Province, highlighting the c. 1200–1120 Ma Musgravian Orogeny that affected the entire province (e.g. Camacho and Fanning 1995; Aitken and Betts 2009; Smithies et al. 2011; Tucker et al. 2015; Wong et al. 2015), the c. 1090–1040 Ma extensional Giles Event, and the c. 600–540 Ma transpressional Petermann Orogeny that resulted in the current east–west-trending grain of the province (e.g. Raimondo et al. 2010; Walsh et al. 2013; Maier et al. 2015). In addition, younger reworking is also documented in the form of shear zone reactivation and localised deformation during the long-lived but apparently episodic c. 450–300 Ma Alice Springs Orogeny (Haines, Hand and Sandiford 2001; Buick, Storkey and Williams 2008).
However, the thermochronological record of the younger events is not well studied or constrained. In particular, no low-temperature thermochronological studies have been conducted to investigate the timing of exhumation to shallow crustal levels.
Sample rationale and methods
The purpose of the study was to examine the exhumation history across the east-trending structural grain of the eastern Musgrave Province. Specifically, the study aimed to test the hypothesis that the Petermann and Alice Springs orogenies were the main causes for Phanerozoic exhumation in the region. In addition, the research aimed to test if any thermal events occurred subsequent to the Alice Springs Orogeny. To achieve this, a suite of samples was collected from Paleo- and Mesoproterozoic granitoids in a northeast-trending traverse across the Marryat and Coglin faults (Fig. 1). This aimed to evaluate potential exhumation across these structures. Methods used were apatite fission track, and apatite and zircon (U–Th–Sm)/He, along with U–Pb dating of apatite, a technique with closure temperatures of between ~450 °C and ~550 °C.
Apatite U–Pb dating on six samples yielded consistent results of c. 1075–1025 Ma. Apatite fission track analysis indicates that several discrete thermal events affected the study area, inducing cooling through apatite fission track closure temperatures (~60–120 °C), and is supported by additional apatite and zircon (U–Th–Sm)/He data. These events occurred during the: Late Neoproterozoic (c. 550 Ma), when cooling from deep crustal levels to temperatures <200 °C occurred; Silurian–Devonian (c. 450–400 Ma); Late Carboniferous (c. 310–290 Ma); and Triassic – Early Jurassic (localised).
Discussion and conclusion
The data reveals four thermal events, described below, that affected the eastern Musgrave Province.
- Thermal resetting of granites to temperatures up to ~500 °C occurred during mantle-derived magmatism of the Giles Event (c. 1090–1040 Ma).
- Neoproterozoic cooling is likely to be related with exhumation and denudation during the Petermann Orogeny.
- The Silurian–Devonian and Late Carboniferous cooling phases suggest there were several phases of cooling during the Alice Springs Orogeny. These are likely associated with the exhumation of granitoids of the eastern Musgrave Province to shallow crustal depths.
- A Triassic – Early Jurassic thermal event observed throughout the study area is thought to be related to elevated geothermal gradients at that time. However, more data is needed to further constrain this potential Mesozoic thermal event.
The high sample density across the structural architecture of the study area also reveals patterns of fault reactivation and resulting differential exhumation.
The results indicate shallower exhumation levels in the centre that are represented by younger apatite fission track ages (c. 250 Ma), and deeper exhumation towards the margins of the transect where older apatite fission track ages (c. >300 Ma) are recorded (Figs 1, 2). The observed differential exhumation patterns match with existing seismic data and fit a model of an inverted graben system between the Coglin and Marryat faults. Furthermore, the data suggests that the reactivation of this graben system occurred relatively late in the Alice Springs Orogeny.
The results highlight that the eastern Musgrave Province records a complex Phanerozoic low-temperature thermal history, revealing the poorly appreciated tectonic evolution of inland Australia. The study also shows the value of low-temperature thermochronology as a tool for understanding the fault and exhumation history of an area.
Rian Dutch, James Hall, Martin Danišík, Noreen Evans and Alan Collins were part of the team for the original study and are acknowledged for their input. Anthony Reid provided a review for this article.
Aitken ARA and Betts PG 2009. Multi-scale integrated structural and aeromagnetic analysis to guide tectonic models: an example from the eastern Musgrave Province, central Australia. Tectonophysics 476(3–4):418–435.
Buick IS, Storkey A and Williams IS 2008. Timing relationships between pegmatite emplacement, metamorphism and deformation during the intra-plate Alice Springs Orogeny, central Australia. Journal of Metamorphic Geology 26:915–936.
Camacho A and Fanning CM 1995. Some isotopic constraints on the evolution of the granulite and upper amphibolite facies terranes in the eastern Musgrave Block, central Australia. Precambrian Research 71(1–4):155–181.
Ehlers TA and Farley KA 2003. Apatite (U–Th)/He thermochronometry: methods and applications to problems in tectonic and surface processes. Earth and Planetary Science Letters 206(1–2):1–14.
Glorie S, Agostino K, Dutch R, Pawley M, Hall J, Danišík M, Evans NJ and Collins AS 2017. Thermal history and differential exhumation across the eastern Musgrave Province, South Australia: insights from low-temperature thermochronology. Tectonophysics 703–704:23–41.
Green PF, Duddy IR, Gleadow AJW, Tingate PR and Laslett GM 1985. Fission track annealing in apatite: track length measurements and the form of the Arrhenius plot. Nuclear Tracks and Radiation Measurements 10:323–328.
Haines PW, Hand M and Sandiford M 2001. Palaeozoic synorogenic sedimentation in central and northern Australia: a review of distribution and timing with implications for the evolution of intracontinental orogens. Australian Journal of Earth Sciences 48:911–928.
Hall JW, Glorie S, Collins AS, Reddy M, Trenouth C, Evans N and Reid AJ 2016a. Low-temperature thermal histories of the northern and eastern Gawler Craton. Australian Earth Sciences Convention, 26-30 June 2016, Abstracts Volume, p. 181.
Hall JW, Glorie S, Collins AS, Reid A, Evans N, McInnes B and Foden J 2016b. Exhumation history of the Peake and Denison Inliers: insights from low-temperature thermochronology. Australian Journal of Earth Sciences 63(7):805–820.
Howard HM, Smithies RH, Kirkland CL, Kelsey DE, Aitken A, Wingate MTD, Quentin de Gromard R, Spaggiari CV and Maier WD 2015. The burning heart — The Proterozoic geology and geological evolution of the west Musgrave Region, central Australia. Gondwana Research 27(1):64–94.
Maier WD, Howard HM, Smithies RH, Yang SH, Barnes SJ, O'Brien H, Huhma H and Gardoll S 2015. Magmatic ore deposits in mafic-ultramafic intrusions of the Giles Event, Western Australia. Ore Geology Reviews 71:405–436.
Raimondo T, Collins AS, Hand M, Walker-Hallam A, Smithies RH, Evins PM and Howard HM 2010. The anatomy of a deep intracontinental orogen. Tectonics 29(4).
Smithies RH, Howard HM, Evins PM, Kirkland CL, Kelsey DE, Hand M, Wingate MTD, Collins AS and Belousova E 2011. High-temperature granite magmatism, crust–mantle interaction and the Mesoproterozoic intracontinental evolution of the Musgrave Province, central Australia. Journal of Petrology 52(5):931–958.
Smithies RH, Kirkland CL, Korhonen FJ, Aitken ARA, Howard HM, Maier WD, Wingate MTD, Quentin de Gromard R and Gessner K 2015. The Mesoproterozoic thermal evolution of the Musgrave Province in central Australia - plume vs. the geological record. Gondwana Research 27(4):1419–1429.
Tucker NM, Hand M, Kelsey DE and Dutch RA 2015. A duality of timescales: short-lived ultrahigh temperature metamorphism preserving a long-lived monazite growth history in the Grenvillian Musgrave-Albany-Fraser Orogen. Precambrian Research 264:204–234.
Wade BP, Kelsey DE, Hand M and Barovich KM 2008. The Musgrave Province: stitching north, west and south Australia. Precambrian Research 166(1–4):370–386.
Wagner GA and Van den haute P 1992. Fission track-dating. Dordrecht, Kluwer Academic Publishers.
Walsh AK, Raimondo T, Kelsey DE, Hand M, Pfitzner HL and Clark C 2013. Duration of high-pressure metamorphism and cooling during the intraplate Petermann Orogeny. Gondwana Research 24(3–4):969–983.
Wolfe MR and Stockli DF 2010. Zircon (U–Th)/He thermochronometry in the KTB drill hole, Germany, and its implications for bulk He diffusion kinetics in zircon. Earth and Planetary Science Letters 295:69–82.
Wong BL, Morrissey LJ, Hand M, Fields CE and Kelsey DE 2015. Grenvillian-aged reworking of late Paleoproterozoic crust of the southern North Australian Craton, central Australia: implications for the assembly of Mesoproterozoic Australia. Precambrian Research 270:100–123.
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